Deep inside a NationsBank Corp. building, dozens of  programmers are writing and rewriting computer code. 
They are working on the machinery of the $500 million "model bank"  project. 
  
NationsBank officials say the program has already contributed to a 20%  increase in sales per full-time employee in certain areas, and there is   more to come.   
Model banking "gives us an incredible competitive advantage," said H.  Rusty Rainey, the NationsBank executive vice president overseeing the   project. "This is the foundation piece for our future."   
  
The technology gives employees access to a vast data base of sales and  service information on 13 million customers. Nifty new desktop computers   provide prompts to sales associates in branches, then the screens can be   turned so that customers can see product offerings and compare prices.     
This month, further enhancements will allow bank employees to move  beyond basic account information and into such details as small-business   loans, asset management, mortgages, and investments, Mr. Rainey said.   
Model banking encompassed a streamlining of management, redesigns of  products and services, and automating more than 200 branch functions. A   checking account that may have once taken 15 minutes to open takes less   than a minute now.     
  
The program's linchpin is a unification of software and hardware.  Inconsistencies and incompatibilities among several hundred computer   systems are being smoothed out.   
The "core technology architecture" and development of common processes  and products will allow NationsBank to become truly national, said Mr.   Rainey. Now customers in each of the 16 states where it operates can   receive a "consistent customer experience."     
Analysts expressed enthusiasm about the project.
"It enhances revenue and saves costs," said Sally Pope Davis of Goldman  Sachs & Co. "This is definitely one of the most cutting-edge programs out   there."   
  
David Hilder of Morgan Stanley & Co. said it is difficult to calculate  how much model banking will contribute to company earnings. But its goals-   common systems and detailed customer relationship information-are beyond   reproach.     
"Ultimately, the results of this will show up in higher income levels, a  better efficiency ratio, and probably better returns on assets and equity,"   he said.   
NationsBank plans to spend about $100 million on model banking this year  and another $50 million to $75 million in 1998. 
The Charlotte-based company started putting the model banking technology  in place in late 1995 in Georgia and has nearly completed the   infrastructure in the states in which it operated before acquiring St.   Louis-based Boatmen's Bancshares in January.     
Company programmers finished installations in the Carolinas in March and  are now focusing on Texas, which is to be fully operational by October.   Work on the former Boatmen's, with its 626 branches in the Midwest, won't   be finished until July 1998.     
NationsBank is also putting model banking technology in its telephone  service and sales centers. It is installing a system that will enable   personnel working the phones to pull up the same customer information that   banking-center sales associates have.     
The technology is coming on line this month in Florida; NationsBank  operates a call center in Tampa. The middle-Atlantic region will be next   this summer, when NationsBank brings the systems to Baltimore, Washington,   and Virginia. u